linux-kernel - Re: RAID array is gone, please help

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Date:   Thu, 23 Mar 2017 22:02:23 +0100
From:   Stephen Mueller <stephen@...ller.org>
To:     Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: RAID array is gone, please help

Looks like it worked! Thanks!

I used:

sudo mdadm --create /dev/md0 --assume-clean --verbose --level-10 
--raid-devices=4 /dev/sdc /dev/sdd /dev/sde /dev/sdf

And I got my instructions for creating the array here, and they
also don't use partitions...

https://www.digitalocean.com/community/tutorials/how-to-create-raid-arrays-with-mdadm-on-ubuntu-16-04


On 3/23/2017 21:09, Stephen Mueller wrote:
> OK, I used gdisk to remove the GPT and MBR from each disk.
> mdadm --assemble still doesn't work... says it can't find the
> superblock. The mdadm --examine commands also say that no
> superblock is detected.
>
> I guess I'll go ahead with --create...
>
>
> On 3/23/2017 20:59, Lennart Sorensen wrote:
>> On Thu, Mar 23, 2017 at 08:38:08PM +0100, Stephen Mueller wrote:
>>> Apologies, I should have started this on linux-raid...
>>>
>>>
>>> stephen@...d> sudo gdisk -l /dev/sdc
>>> GPT fdisk (gdisk) version 1.0.1
>>>
>>> Partition table scan:
>>>   MBR: protective
>>>   BSD: not present
>>>   APM: not present
>>>   GPT: present
>>>
>>> Found valid GPT with protective MBR; using GPT.
>>> Disk /dev/sdc: 7814037168 sectors, 3.6 TiB
>>> Logical sector size: 512 bytes
>>> Disk identifier (GUID): 60F1D54C-9D17-4688-BD6E-447F5E7408EB
>>> Partition table holds up to 128 entries
>>> First usable sector is 34, last usable sector is 7814037134
>>> Partitions will be aligned on 2048-sector boundaries
>>> Total free space is 7814037101 sectors (3.6 TiB)
>>>
>>> Number  Start (sector)    End (sector)  Size       Code  Name
>>> stephen@...d>
>>>
>>> The other disks are all similar.
>>>
>>> How do I remove the MBR/GPT tables? So you would do that, and then the
>>> mdadm --create?
>>
>> Well at least that seems to confirm that something restored the GPT from
>> the second copy at the end of the disk, wiping out the md superblock
>> at 4k.
>>
>> If you run gdisk /dev/sdc, it has a 'zap' option using the z key to
>> delete all traces of GPT.  That ought to do what you want.
>>